Working on a Rheem natural gas furnace. It's got the "jet" type burners. Four burners. 80 percenter.
The inducer blows, the HSI heats, the gas lights. And lights all the way across. About a second later, the gas shuts off. And, the whole thing goes through the routine again.
The call came in Friday about 6 PM. Didn't have a sensor rod, so Monday I bought one.
Now, even with a new sensor rod, and a new grounding screw, it's still the same. Fires for a second, and then shuts down.
The furnace is a 1999 model now. Has had essentially no maint except for filter changes.
I checked the ground to neutral at the furnace (less than one ohm) and the connection between the terminal and the molex connector where it comes off the main board. Also less than one ohm. Then checked the ground screw from the sensor rod to the 110 VAC ground. Again, nothing.
Guess the only grounding thing I didn't check was that the ground wire from the 110 VAC was connected to the case of the furnace. Is that relevant?
What else to check, or is it time to replace the board?